Molded paper bodies have hitherto been universally used in various forms of containers in the field of packaging and containers. There are one-piece molded paper bodies such as paper trays or paper dishes, and there are two-piece paper containers formed of a body member and a bottom member.
Molded paper bodies formed by deep drawing a blank that is mainly made of paper lack malleability and ductility unlike metals and the blank tends to wrinkle in upright portions along the periphery during the process. FIG. 10 shows a two-piece paper container consisting of a bottom member X and a body member Y. The bottom member (Molded paper body) is formed by deep drawing. The following methods have been disclosed as techniques to reduce wrinkles in molded paper bodies.
Patent Document 1 discloses a method of deep drawing for producing pressed paper containers wherein a flange press and a die upper surface are kept a constant distance from each other to enable deep drawing with minimal wrinkling. Patent Document 2 aims at providing a bottom piece for paper cups that can make favorable tight contact with the body member and discloses a method wherein an outer peripheral portion of the bottom piece is pressed from above. Patent Document 3 aims at providing a bottom piece for paper cups that has pleats (wrinkles) not so large as to be folded and discloses a deep drawing method wherein the gap between a drawing part (punch) and an opening (die) is made smaller than the thickness of the paper stock (blank).
Patent Document 1: Japanese Patent No. 4121832 “Method and apparatus for producing molded container and molded container” registered on May 9, 2008 and issued on Jul. 23, 2008
Patent Document 2: Japanese Patent Application Laid-open No. 2001-270013 “Apparatus and method for forming bottom paper sheet of paper cup” published on Oct. 2, 2001
Patent Document 3: Japanese Patent Application Laid-open No. 2000-238150 “Paper cup bottom and method and apparatus for forming same”, published on Sep. 5, 2000